我需要从另一个对象数组的另一个键中减去一个对象数组的键

Question

我有接下来的两个数组：

const firstArray = [{startDate: 5, number: 15}, {startDate: 25, number: 10}, {startDate: 26, number: 10}];
const secondArray= [{startDay: 2, endDay:10, number: 15}, {startDay: 20, endDay:30, number: 20}];

如果 startDate 介于 startDay 和 endDay 之间，我必须减去 firstArray number 和 secondArray number 用结果创建新密钥

因此，我必须将新键放入 firstArray 中，结果为：

const firstArray = [{startDate: 5, number: 15, result: 0}, {startDate: 25, number: 25, result: -10}, {startDate: 26, number: 25, result: 0}];

如果我在同一范围内（在 startDay 和 endDay 之间）有多个 startDate，我必须添加到该范围的最后一个结果

我现在拥有的代码：

firstArray.map(el => ({...el, result: el.number - here's number from the secondArray according to the requirements}))

Answer 1

Map 在循环两个数组和改变值时效果不佳。

只需使用简单的for 循环，检查firstArray[i] 和secondArray[i] 之间的条件，然后将值添加到firstArray[i].result

const firstArray = [{startDate: 5, number: 15}, {startDate: 25, number: 20}];
const secondArray= [{startDay: 2, endDay:10, number: 10}, {startDay: 20, endDay:30, number: 20}];

for (let i = 0; i < Math.min(firstArray.length, secondArray.length); i++)
  if (secondArray[i].startDay < firstArray[i].startDate && firstArray[i].startDate < secondArray[i].endDay)
    firstArray[i].result = firstArray[i].number - secondArray[i].number;
    
console.log(firstArray);

Answer 2

当您使用两个或多个数组时，您需要知道您正在使用哪个索引。此外，为了获得最佳性能，请避免使用任何类型的回调函数，而是使用简单的循环：

const firstArray = [{startDate: 5, number: 15}, {startDate: 25, number: 10}, {startDate: 26, number: 10}];
const secondArray= [{startDay: 2, endDay:10, number: 15}, {startDay: 20, endDay:30, number: 20}];

for(let i = 0, first, second, result = 0; i < firstArray.length; i++)
{
  first = firstArray[i];
  second = secondArray[i];
  if (second && first.startDate >= second.startDay && first.startDate <= second.endDay)
    result = first.number - second.number;
  else
    result += first.number;

  first.result = result;
}

console.log(firstArray);

使用map() 也可以，生成的代码稍微短一些，但速度较慢且非常不必要：

const firstArray = [{startDate: 5, number: 15}, {startDate: 25, number: 10}, {startDate: 26, number: 10}];
const secondArray= [{startDay: 2, endDay:10, number: 15}, {startDay: 20, endDay:30, number: 20}];

firstArray.map((first, i) =>
{
  const second = secondArray[i];
  if (second && first.startDate >= second.startDay && first.startDate <= second.endDay)
    first.result = first.number - second.number;
  else
    first.result = ((firstArray[i-1]||{}).result || 0) + first.number;

});

console.log(firstArray);